Embedded capacitive stack

ABSTRACT

A novel method for manufacturing embedded a capacitive stack and a novel capacitive stack apparatus are provided having a capacitive core that serves as a structural substrate on which alternating thin conductive foils and nanopowder-loaded dielectric layers may be added and tested for reliability. This layering and testing allows early fault detection of the thin dielectric layers of the capacitive stack. The capacitive stack may be configured to supply multiple isolated capacitive elements that provide segregated, device-specific decoupling capacitance to one or more electrical components. The capacitive stack may serve as a core substrate on which a plurality of additional signaling layers of a multilayer circuit board may be coupled.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

The present Application for Patent claims priority to ProvisionalApplication No. 60/894198 entitled “Embedded Capacitive Stack” filedMar. 10, 2007 and is hereby expressly incorporated by reference herein.

FIELD

Various embodiments of the invention pertain to circuitboards/substrates, chip package substrates, backplanes, flex and rigidcircuits, and electronic modules. At least one embodiment of theinvention pertains to an embedded capacitive stack for multilayercircuit boards.

BACKGROUND

Electronic circuit devices are commonly used in both digital and analogcircuits. In digital signal processing, signals change from one binarylevel to another. Such signals often become distorted due to resistance,capacitance, and/or inductance along its path on a circuit board.Moreover switching from one binary level to another often gives rise tostill other distortions and spurious signals, e.g., noise, and inducedsignals on other electrical paths on the circuit board. In the art ofcircuit design and circuit board manufacturing, capacitors are commonlyemployed in order to reduce electromagnetic interference, decouplesignals, reduce or dampen resonances, suppress current/voltage noise,improve signal quality, filter signals, and several further suchpurposes and/or functions.

Historically, discrete bypass capacitors have been used with specificactive devices for high-frequency decoupling (e.g., resonance dampening,noise suppression, etc.) and still are employed when designers do notface space constraints. However, with the increased complexity ofcircuits and the reduction in the size of electronic products, the spaceon the surface of a circuit board is often limited and does not allowroom for numerous surface mounted decoupling capacitors. Additionally,the electrical vias required by the discrete capacitors introduceunwanted parasitic inductance at higher frequencies. Consequently, anembedded decoupling capacitance (or buried capacitance) is typicallyused to eliminate the need for bypass capacitors mounted in the vicinityof each integrated circuit mounted to the board.

Attempts at providing embedded decoupling capacitance are known in theart. For example, in U.S. Pat. No. 5,079,069 to Howard et al, anintegral buried capacitor is provided comprising a sheet of dielectricmaterial that is sandwiched between two sheets of conductive material.Howard, thus, discloses a printed circuit board (PCB) that providescapacitance to each individual device by a portion of the capacitorlaminate proportional to the individual device and borrowed capacitancefrom other portions of the capacitor laminate, depending upon the randomoperation of the devices.

While PCBs using an integrated capacitive laminate, such as the onedisclosed by Howard et al., are generally successful in providingcapacitance to a device, in certain applications the capacitancesupplied by such integrated capacitive laminates is limited orinsufficient. For example, because of their potential for interferenceand noise, certain high power, high switching speed integrated circuit(IC) devices often demand a decoupling capacitance that exceeds thatwhich can be supplied by integrated capacitive laminates similar tothose disclosed by Howard et al. In those circumstances, circuitdesigners employ additional localized, surface mounted capacitors inorder to provide sufficient decoupling capacitance for the IC device.Such localized, surface mounted capacitors, however, are undesirable forthe reasons discussed above.

Prior art capacitor laminates also suffers from a further deficiency inthat the electronic device are all connected to the same embeddedcapacitive laminate, causing potential interference between devices. Forinstance, high power, high switching speed IC devices may causesignificant voltage and/or current variations, or noise that potentiallyinterferes with other low-noise devices on the circuit board that mayalso be coupled to the capacitive laminate.

In order to deal with the increased capacitance needs of high power,high switching speed IC devices, integrated capacitive laminates withincreased capacitance have been developed, wherein several laminates arestacked together and connected in parallel. U.S. Pat. No. 6,739,027 toLauffer et al., for example, discloses a capacitive PCB that isfabricated by taking a first conductive foil and coating both sides witha dielectric. Second and third conductive foils are also coated with adielectric on one side and each foil is attached to the first dielectriccoated foil by the uncoated side of the second and third foils. Thesecond and third foils are each then laminated to a circuitized corecreating four total capacitive planes that are connected in parallelwith each other thereby increasing the capacitance density.

Thus, Lauffer et al., like Howard et al., provides a PCB that suppliescapacitance to each individual device by a portion of the capacitorlaminate proportional to the individual device and borrowed capacitancefrom other portions of the capacitor laminate, depending upon the randomfiring of the devices. Although Lauffer et al. increases the capacitivedensity, the devices still share the same capacitor laminate.Consequently, low-noise devices continue to be subject to interferencefrom the noise produced by the high power, high switching speed ICdevices described above.

Use of a thin dielectric layer made from powdered resin materials orfilled resin systems are known in the art for their high dielectricconstants that makes it possible to increase capacitance density.Lauffer et al. discloses a PCB incorporating the use of a thin,non-cured (B-stage) dielectric. However, the process of manufacturingstacked integrated capacitive laminates disclosed by Lauffer et al.becomes difficult when using these thin dielectrics. The nanopowderloading in thin dielectrics is very brittle and virtually impossible tomanufacture without special handling and processing. Furthermore, usinga thin dielectric creates the increased possibility that the conductivefoils that sandwich the dielectric will have inclusions or voids thatcompromise the electrical integrity, creating a short in the capacitorand risk starting a fire. Testing for shorts is not possible until thestacked capacitive element is finished. If a defect is discovered theentire PCB must be scrapped, resulting in a potentially high monetaryloss.

Thus, there remains a long felt need in the art for providing stackedintegrated or embedded capacitors with very thin dielectric thicknessand high Dk due to nanoloading on a circuit board capable of beingconnected in parallel in order to increase capacitance density oralternatively capable of providing separate capacitance for noisierdevices and quieter devices. There is also a long felt need to identifyfaults and defects in a stacked capacitive core before adding subsequentcore layers or circuit layers are added.

SUMMARY

One feature provides a method for manufacturing a capacitive stack withhigh capacitive density. A planar core capacitive substrate is formedincluding a first dielectric core layer sandwiched between a firstconductive layer and a second conductive layer. The core capacitivesubstrate may provide structural rigidity for coupling additionalconductive and dielectric layers. A first conductive foil may be coatedwith a second dielectric layer that may include an uncured or semi-cureddielectric material loaded with a nanopowder selected to achieve adesired dielectric constant. An exposed surface of the second dielectriclayer may be coupled to the first conductive layer and the dielectricmaterial of the second dielectric layer may then be cured.

A pattern of one or more clearances may be formed on the firstconductive layer. The one or more clearances on the first conductivelayer may be filled with an epoxy prior to coupling the seconddielectric layer to the first conductive layer. The epoxy may be curedprior to coupling the second dielectric layer to the first conductivelayer. The epoxy may be planarized prior to coupling the seconddielectric layer to the first conductive layer.

Additionally, a second conductive foil may be coated with a thirddielectric layer that may include an uncured or semi-cured dielectricmaterial loaded with a nanopowder selected to achieve a desireddielectric constant. An exposed surface of the third dielectric layermay be coupled to the second conductive layer and the dielectricmaterial of the third dielectric layer is cured.

The first conductive foil and first conductive layer may define a firstcapacitive element and the second conductive foil and second conductivelayer may define a second capacitive element. A first electricallyconductive via may be formed between the first conductive layer andsecond conductive foil. Similarly, a second electrically conductive viamay be formed between the second conductive layer and first conductivefoil. A capacitive element having increased capacitive density may beformed between the first conductive layer-second conductive foil and thesecond conductive layer-first conductive foil.

In another example, a first isolated capacitive element may be formedbetween the first conductive layer and the first conductive foil. Asecond isolated capacitive element may be formed between the secondconductive layer and the second conductive foil. Likewise, a thirdisolated capacitive element may be formed between the first conductivelayer and the second conductive layer.

According to one feature, one or more alternating conductive foils anddielectric layers may be coupled on at least one side of the corecapacitive substrate. The integrity of the dielectric layers may betested as they are stacked onto the core capacitive substrate.

In some examples, the second dielectric layer may include a dielectricfilm, and coating the first conductive foil with the second dielectriclayer may include laminating the dielectric film on the first conductivefoil.

According to some examples, the thickness of the second dielectric layermay be less than the thickness of first dielectric layer. The seconddielectric layer may be coated to a thickness of approximately between0.004 mil and 1.25 mil. In one example, the second dielectric layer maybe coated to a thickness of approximately 0.3 mil or less. The firstconductive foil and second conductive foil may be ultra-thin foils ofhaving a thickness of 0.12 mil and 4 mil. The core capacitive substratemay have a thickness of approximately between 0.25 mil and 4 mil. Thesecond dielectric layer may provide a capacitive density of between five(5) and sixty (60) nano-Farads per square inch.

According to another example, a first region on the first conductivefoil is formed that is electrically isolated from the remaining portionsof the first conductive foil. The first region and the first conductivelayer may form a capacitive element distinct from the remaining portionsof the first conductive foil and first conductive layer. The size of thefirst region and a capacitive density of the second dielectric layer areselected to achieve a desired capacitive value.

Consequently, a capacitive stack with high capacitive density isprovided comprising: (a) a planar core capacitive substrate including afirst core dielectric layer sandwiched between a first conductive layerand a second conductive layer, wherein the core capacitive substrateprovides structural rigidity for coupling additional conductive anddielectric layers; (b) a second dielectric layer having a first planarsurface coupled to the first conductive layer, the second dielectriclayer being thinner than the first core dielectric layer and including adielectric material loaded with a nanopowder selected to achieve adesired dielectric constant; (c) a first conductive foil coupled to asecond planar surface of the second dielectric layer; wherein thethickness of the second dielectric layer is less than the thickness offirst dielectric layer; and/or (d) one or more alternating conductivefoils and dielectric layers coupled on at least one side of thecapacitive core substrate. The first and second conductive layers andthe first conductive foil may be alternating power and ground planes. Atleast one of the first and second conductive layers may include apattern of one or more clearances. In one example, the second dielectriclayer is coated to a thickness of approximately between 0.004 and 1.25mil. In another example, the first conductive foil may be an ultra-thinfoil having a thickness of between 1 and 4 mil or a thickness of between0.12 and 1 mil. The second dielectric layer may provide a capacitivedensity of between five (5) and sixty (60) nano-Farads per square inch.

A method for manufacturing a multilayer embedded capacitive stack isalso provided. A planar core capacitive substrate is formed including afirst dielectric core layer sandwiched between a first conductive layerand a second conductive layer. The core capacitive substrate providesstructural rigidity for additional conductive and dielectric layers. Afirst conductive foil is coated with an uncured or semi-cured dielectricmaterial to form a second dielectric layer. The uncured or semi-cureddielectric material may be loaded with a nanopowder selected to achievea desired dielectric constant. The second dielectric layer may becoupled to the first conductive layer and the integrity of the seconddielectric layer may be tested. The capacitive stack may be discarded ifa defect is found in the second dielectric layer. The second dielectriclayer may have a defect if the first conductive layer and firstconductive foil are electrically coupled. The second dielectric layermay also have a defect if the impedance between the first conductivelayer and first conductive foil is less than a desired threshold value.Coupling an exposed surface of the second dielectric layer to the firstconductive layer may include using an epoxy layer between the seconddielectric layer to the first conductive foil. The integrity of thesecond dielectric layer is tested prior to coupling additional layersonto the first conductive foil.

Additionally, a second conductive foil may be coated with the uncured orsemi-cured dielectric material to form a third dielectric layer. Anexposed surface of the third dielectric layer may be coupled to thesecond conductive layer and the integrity of the third dielectric layermay be tested. The exposed surface of the third dielectric layer may becoupled to the second conductive layer at the same time that the exposedsurface of the second dielectric layer is coupled to the firstconductive layer. The integrity of the second dielectric layer and thethird dielectric layer may be tested at the same time.

Similarly, one or more alternating conductive foils and dielectriclayers may be coupled on at least one side of the core capacitivesubstrate. The integrity of each dielectric layer may be tested as it isadded to the capacitive stack.

In an alternative method for manufacturing a multilayer embeddedcapacitive stack, a planar capacitive core substrate is formed includinga core first dielectric layer sandwiched between a first conductivelayer and a second conductive layer, wherein the core capacitivesubstrate provides structural rigidity for additional conductive anddielectric layers. The first conductive layer is coated with an uncuredor semi-cured dielectric material to form a second dielectric layer,wherein the uncured or semi-cured dielectric material is loaded with ananopowder selected to achieve a desired dielectric constant. A firstconductive foil may be coupled onto an exposed surface of the seconddielectric layer and the integrity of the second dielectric layer istested.

Consequently, a capacitive stack is provided comprising: (a) a planarcapacitive core substrate including a first dielectric layer sandwichedbetween a first conductive layer and a second conductive layer, whereinthe first dielectric layer provides structural rigidity for additionalconductive and dielectric layers; (b) a second dielectric layersandwiched between a first conductive foil and the first conductivelayer, wherein the second dielectric layer is thinner than the firstdielectric layer and includes dielectric material loaded with ananopowder; (c) a first isolated capacitive element defined between thefirst conductive layer and the second conductive layer; (d) a secondisolated capacitive element defined between the first conductive foiland the first conductive layer; (e) a third dielectric layer sandwichedbetween the second conductive layer and a second conductive foil; and/or(f) a third isolated capacitive element defined between the secondconductive layer and the second conductive foil. A first electricallyconductive via may be coupled between the first conductive layer andsecond conductive foil and a second electrically conductive via may becoupled between the second conductive layer and first conductive foil toform a capacitive element having increased capacitive density betweenthe first conductive layer and second conductive foil and the secondconductive layer and first conductive foil.

The first conductive layer and second conductive foil may serve as powerlayers while the second conductive layer and first conductive foil serveas ground layers.

In one example, the thickness of the second dielectric layer is lessthan the thickness of first dielectric layer. For instance, the firstdielectric layer may have a thickness of approximately between 0.5-4mils, the first and second conductive layers may each have a thicknessof between 0.5-6 mils, the second dielectric layer may have a thicknessof approximately between 0.08 and 1.25 mil (or between 0.004 and 1 milor approximately 0.3 mil or less), and the first conductive foil mayhave a thickness of approximately between 0.25-1.5 mils (or between 1and 4 mil or between 0.12 and 1 mil). The first conductive foil mayinclude a first region electrically isolated from the first conductivefoil, wherein the first region and the first conductive layer define afirst discrete capacitive element. The area of the first region may beselected to obtain a desired capacitive value for the first discretecapacitive element.

A method for manufacturing electronic interconnect platform is alsoprovided comprising (a) forming a planar embedded capacitive stack and(b) coupling one or more signal layers on at least one side of theembedded capacitive stack. The capacitive stack may include (a) a planarcore capacitive substrate including a first dielectric layer sandwichedbetween a first conductive layer and a second conductive layer, whereinthe core capacitive substrate provides structural rigidity foradditional conductive layers and thinner dielectric layers; (b) one ormore alternating dielectric layers and conductive foils coupled on atleast one side of the planar core capacitive substrate, wherein the oneor more dielectric layers include a dielectric material loaded with ananopowder and are thinner than the first dielectric layer; (c) whereinthe first, and second conductive layers and the one or more alternatingdielectric layers and conductive foils are adapted to operate assegregated capacitive elements. A first region may be formed in a firstconductive foil from among the one or more conductive foils that iselectrically isolated from the third conductive foil. The first regionand an adjacent conductive layer may define a first segregatedcapacitive element electrically distinct from the remaining portions ofthe first conductive foil. This method may also be used to form achip-scale package may be formed that houses the planar embeddedcapacitive stack and the one or more signal layers.

Consequently, an electronic interconnect platform is provided comprisinga planar embedded capacitive stack and one or more signal layers coupledon at least one side of the embedded capacitive stack. The embeddedcapacitive stack may include (a) a planar capacitive core substrateincluding a first dielectric layer sandwiched between a first conductivelayer and a second conductive layer, wherein the first dielectric layerprovides structural rigidity for additional conductive and dielectriclayers; (b) one or more alternating dielectric layers and conductivefoils coupled on at least one side of the planar capacitive coresubstrate, wherein the one or more dielectric layers include adielectric material loaded with a nanopowder; and/or (c) wherein thefirst and second conductive layers and the one or more alternatingdielectric layers and conductive foils are configurable to operate assegregated capacitive elements.

The electronic interconnect platform may also include a first circuitcomponent coupled to an exterior signal layer and electrically coupledto a first segregated capacitive element formed between a firstconductive foil and the first conductive layer in the embeddedcapacitive stack. The first circuit component may be further coupled toa second segregated capacitive element formed between the firstconductive layer and a second conductive foil in the embedded capacitivestack, the second segregated capacitive element being distinct from thefirst segregated capacitive element. The electronic interconnectplatform may further include a chip-scale package housing the planarembedded capacitive stack, the one or more signal layers, and the firstcircuit component. Additionally, a first region in a third conductivefoil from among the one or more conductive foils may be electricallyisolated from the third conductive foil, and the first region and anadjacent conductive foil may define a first discrete capacitorelectrically isolated from the remaining portions of the thirdconductive foil.

Other features and advantages of the present invention will becomeapparent in the following detailed description of the preferredembodiment of the invention taken in conjunction with the accompanyingdrawings and examples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the construction of a core capacitive element thatmay be used as part of a stacked capacitor according to one example.

FIG. 2 illustrates the addition of capacitive layers to the corecapacitive element to form a capacitive stack having increasedcapacitive density according to one example.

FIG. 3 illustrates a method for manufacturing an embedded corecapacitive stack according to one example.

FIG. 4 illustrates a method for manufacturing an embedded corecapacitive stack according to one example.

FIG. 5 illustrates a capacitive stack including a single capacitiveelement on the bottom of a core capacitive element and two capacitiveelements on top of the core capacitive element.

FIG. 6 illustrates how a core capacitive stack may be configured toprovide a planar capacitive element having high capacitive densityaccording to one example.

FIG. 7 illustrates how the capacitive stack may be configured to providea plurality of segregated planar capacitive elements according to oneexample.

FIG. 8 illustrates another example of how a capacitive stack may beconfigured to form a plurality of isolated bypass capacitors to decoupleelectronic components.

FIG. 9 illustrates another example of how a capacitive stack may beconfigured to form a plurality of distinct bypass capacitors to decoupleelectronic components.

FIG. 10 illustrates yet another example of how a capacitive stack may beconfigured to form a plurality of distinct bypass capacitors to decoupleelectronic components on double-sided circuit board.

FIG. 11 illustrates a method for forming isolated decoupling capacitiveelements in a capacitive stack according to one example.

FIG. 12 illustrates an example of how one or more layers of a capacitivestack may be divided to provide additional decoupling capacitance to oneor more circuit components.

FIG. 13 illustrates yet another example of how one or more conductivelayers of a capacitive stack may be divided into different areas orregions that are electrically isolated from other regions on the sameconductive layer.

FIG. 14 illustrates a method for manufacturing a circuit board having anembedded stacked capacitor according to one example.

FIG. 15 illustrates one example of how a capacitive stack may be usedwithin a chip-scale package to provide localized capacitance to asemiconductor device.

DETAILED DESCRIPTION

In the following description numerous specific details are set forth inorder to provide a thorough understanding of the invention. However, oneskilled in the art would recognize that the invention might be practicedwithout these specific details. In other instances, well known methods,procedures, and/or components have not been described in detail so asnot to unnecessarily obscure aspects of the invention.

In the following description, certain terminology is used to describecertain features of one or more embodiments of the invention. Forinstance, “core” refers to a substrate that mechanically supports one ormore layers. The “core” may include one or more base layers to which oneor more circuit board layers are coupled on one or both sides. The term“embedded” refers to a location below the surface of a printed circuitboard. The term “foil” refers to a thin flexible layer (e.g., lackingstructural rigidity) of metallic and/or electrically conductivematerial. The term “electronic interconnect platform refers to a printedcircuit board, PCB, circuit board, substrate, chip module, and/ormulti-chip module that may include one or more layers of electricallyinsulating material and/or conductive material with conductive tracesand/or vias that provide a base for attaching and/or forming electroniccomponents. As such, these terms include conductive and/or dielectriclayers of all sizes and dimensions used on various applications,including conventional multilayer boards, silicon substrates, chip-scaledevices, chip-scale packaging, semiconductor devices, among others.

A first novel feature provides a way to increase the capacitive densityof a core capacitive stack by stacking thin layers of capacitiveelements (e.g., alternating dielectric layers and conductive foils) on acore capacitive substrate. The dielectric constant of the capacitiveelements may be modified or adjusted by using nanopowder-loaded (resin)dielectric layers between conductive foil layers to increase thecapacitive density of the core capacitive stack. The use of thindielectric layers and conductive foils allows increasing the capacitivedensity while limiting the overall thickness of the capacity stack.

A second novel feature provides a method for manufacturing a capacitivestack is provided that allows capacitive layers to be tested for defectsas they are added to the capacitive stack or as a composite. A coresubstrate is formed having dielectric layer sandwiched between twoconductive layers/foils. The dielectric layer is cured (C-stage) so thatthe core substrate is semi-rigid or rigid, providing a structure ontowhich flexible conductive foils may be laminated. Conductive foils arethen coated with an uncured or partially cured nanopowder loadeddielectric material (B-stage resin) and layered on either side coresubstrate, with the uncured or semi-cured dielectric material adjacentthe conductive layers of the core substrate. Additional conductive foilscoated with the uncured nanopowder loaded dielectric material may belayered, cured, and tested as the multilayered circuit board ismanufactured. This layering, curing, and testing allows early faultdetection of problems with the stacked capacitor.

A third novel feature provides a printed circuit board including acapacitive stack configured to supply segregated, device-specificdecoupling capacitance to one or more devices on the circuit board, amulti-chip module, and/or a semi-conductor package. Thus, insteaddecoupling of all electronic devices on a PCB with a shared embeddedcapacitance, this feature provides multiple isolated capacitive elementscapable of being coupled to different electronic devices.

A fourth novel feature provides for embedding one or more discretecapacitors in a core capacitive stack that may be used within amultilayered circuit board to provide localized decoupling capacitanceto one or more circuit components and/or a semi-conductor package. Theone or more discrete capacitors formed within the core capacitive stackmay be sized to have different values to satisfy the capacitance needsof one or more circuit components and/or semi-conductor device.Additionally, the discrete capacitors may also provide power isolationfor different components. The stacked capacitor may be constructed andtested for reliability as the dielectric layers and conductive foils areadded to the stack prior to embedding the stack into the circuit board.

A fifth novel feature provides for using a capacitive stack within achip-scale package to bring decoupling capacitance closer to a signalsource, thereby reducing undesirable parasitic inductance at higheroperating frequencies.

Increasing Capacitive Density of a Core Capacitive Stack

In the prior art, single capacitive planar cores have been used toprovide decoupling capacitance to circuit boards. However, increasingthe capacitive density of a capacitive core to accommodate decoupling ofhigher frequencies typically requires significantly decreasing thethickness of the capacitive core. This is because increasing thethickness of a capacitive core is undesirable as it increases thethickness of circuit boards and increases parasitic inductance at higherfrequencies.

To address the shortcomings of the prior art, one feature increases thecapacitive density of a core capacitive stack by stacking thin layers ofcapacitive elements (e.g., alternating dielectric layers and conductivefoils) on a core base substrate. The dielectric constant of thecapacitive elements may be modified or adjusted by usingnanopowder-loaded (resin) dielectric layers between conductive layers toincrease the capacitive density of the core capacitive stack.

FIG. 1 illustrates the construction of a core capacitive substrate 100that may be used as part of an embedded capacitive stack according toone example. The core capacitive substrate 100 may include a coredielectric layer 104 sandwiched between a first conductive layer or foil102 and a second conductive layer or foil 106. The core dielectric layer104 may be made from a cured or C-stage dielectric material. Using aC-stage dielectric layer in the core capacitive substrate 100 providesincreased rigidity to subsequent layers of the stacked capacitor. Invarious examples, the core dielectric layer 104 may be (or include)polymide, teflon, epoxy, resin, and/or film. Thus, core capacitivesubstrate 100 serves as a base on which subsequent additional dielectricand conductive layers may be added to create additional capacitiveelements. The first conductive layer 102 and second conductive foil 106may be patterned, either before or after coupling to the core dielectriclayer 104, to form ground and/or power clearances or isolations 108, forexample, that may be subsequently used to electrically connect two ormore conductive layers of the capacitive stack or to couple to one ormore electrical components of a circuit. In some examples, theclearances 108 may be formed, for example, chemical or mechanicalprocessing of the conductive layers 102 and/or 106 such as etching.

The core capacitive substrate 100 may then serve as a rigid orsemi-rigid planar structure or substrate onto which thinner anddifficult-to-process dielectric and/or conductive layers may bealternatively or interchangeably stacked to increase the capacitivedensity.

According some examples and implementations, the dielectric layer 104may be approximately between 0.5 to 4 mils thick and each conductivelayer 102 and 106 may be between 0.25 and 6 mils thick.

In some implementations, a layer 110 and 112 of epoxy or some otherfiller paste (e.g., non-conductive or dielectric material) may be addedto the planar surfaces of the first conductive layers/foils 102 and/or106 to fill-in cavities, voids, and/or clearances 108. Filling thesecavities, voids, and/or clearances 108 may help prevent deformation ofthe subsequent thinner layers that may be stacked and coupled to thecore capacitive substrate. Note that the epoxy or filler paste (e.g.,dielectric paste, epoxy ink, etc.) may be applied, for example, bycoating or dipping and may be of sufficiently thick to fill-in cavities,voids, and/or clearances 108 on the conductive layers 102 and 106. Thefilled clearances are illustrated by reference number 108′.

The epoxy or filler 110 and 112 may then be cured or semi-cured and thenplanarized (e.g., by grinding planarization or other chemical ormechanical processing) to remove excess epoxy or filler paste andprovide a substantially flat surface. Except for the epoxy or pastefiller in the clearances 108′, planarization may completely orsubstantially remove the excess epoxy or paste filler so that thesurface(s) of the conductive layers 102 and/or 106 may be exposed.

FIG. 2 illustrates the addition of capacitive layers to the corecapacitive substrate 100 to form a capacitive stack 200 having increasedcapacitive density according to one example. The capacitive stack 200 isformed by coupling a third conductive foil 202 and a thin firstdielectric layer 204 on one side of the core capacitive substrate 100.The exposed surface of first dielectric layer 204 may be coupled to theexposed surface of the first conductive foil 102 to form a capacitiveelement 210. Similarly, a fourth conductive foil 208 and a thin seconddielectric layer 206 are coupled on an opposite side of the corecapacitive substrate 100. The exposed surface of the second dielectriclayer 206 may be coupled with the exposed surface of the secondconductive foil 106 to form another capacitive element 212. Note that,in some implementations, the third conductive foil 202 and the firstdielectric layer 204 and the fourth conductive foil 208 and the seconddielectric layer 206 may be coupled or added to the core capacitivesubstrate 100 at the same time.

The third conductive foil 202 and fourth conductive foil 208 may bepatterned, e.g., after coupling to the core dielectric layer 104, todefine or form power and/or ground clearances or isolations 214 and 224,for example. Such clearances 214 and 224 may subsequently allow formingappropriate electrical connections to and/or through one or more layersof the capacitive stack 200. Note in some implementations, theclearances 214 and 224 may be filled with an epoxy or filler paste(illustrated as 214′and 224′) prior to coupling additional layers ontothe third conductive foil 202 and fourth conductive foil 208. In otherimplementations, if the third conductive foil 202 and fourth conductivefoil 208 are sufficiently thin, they may simply be filled by the uncureddielectric of a subsequently added dielectric layer.

The dielectric layers 204 and 206 may include a nanopowder-loadeddielectric material. In various examples, the dielectric layers 204 and206 may include dielectric film sheets, gel, liquid, and/or powder. Thedielectric layers 204 and 206 may be coated, laminated and/or coupled tothe conductive foils 202 and 208 (e.g., cooper foils), respectively, byany means known in the industry, such as roller, lamination, screenprinting, powder or curtain coating, spraying, vapor deposition, and/ordipping. Any of these or other known methods may be used in forming athin, substantially uniform dielectric film/layer on a conductive foil.In some implementations, the dielectric layers 204 and/or 206 may be (orinclude) polymers, sol-gels, thin films, in an uncured or semi-curedstate that allow coupling to the core capacitive substrate 100. Notethat, depending on the material used in the dielectric layers 204 and/or206, an additional thin adhesive layer may be added for better adhesionto the core capacitive substrate 100. In one example, the dielectriclayers 204 and/or 206 and/or conductive foils 202 and/or 206 may bequite thin in order to reduce the overall thickness of the capacitivestack 200 and/or printed circuit board in which it is used. Forinstance, the dielectric layers 204 and 206 may each be betweenone-tenth (0.1) and twenty-four (24) micrometers (micron) while theconductive foils 202 and/or 206 may each be between an eighth of anounce (⅛ oz) and six ounce (6 oz) foils. Making the capacitive stack 200and/or printed circuit board as thin as possible is desirable in that itreduces the parasitic inductance associated with the capacitive stack200 at higher frequencies. The capacitive density of the capacitivestack 200 may be increased or decreased by using a nanopowder loadedmaterial of a desired dielectric constant (Dk). For example, ananopowder loaded resin (e.g., Oak MC8TR) may be used to achieve 22nanofarads per square inch. Additionally, the number of capacitivelayers in the capacitive stack may also be increased to increase itscapacitive density. As an example, by utilizing multiple planarcapacitive layers in combination, a total capacitance of 44 nanofaradsper square inch (or more) may be achieved by using the two dielectriclayers 204 and/or 206 (e.g., each layer providing 22 nanofarads persquare inch). Greater capacitive densities may be achieved by selectingan appropriate dielectric material or by increasing the number ofdielectric and conductive layers.

Typically, a thin layer of nanopowder loaded dielectric material isquite brittle and difficult to handle during manufacturing of amultilayer circuit board. However, by depositing or coupling the thindielectric layers 204 and 206 in an uncured or partially cured form onthe substantially rigid core capacitive substrate 100, the integrity ofthe thin dielectric layers 204 and 206 is maintained, thus allowing highyield processing of these conductive foils. Because the core capacitivesubstrate 100 serves as a structural core, the subsequent dielectric andconductive layers can be very thin or ultra-thin, thus making thecapacitive stack and/or the multilayer circuit board in which suchcapacitive stack is embedded thinner than conventional manufacturingtechniques.

The dielectric layers 204 and 206 may be cured when they are coupled tothe core capacitive substrate 100 by heat and/or pressure. Because thethin dielectric layers 204 and/or 206 are cured after they have beencoupled to the substantially rigid core capacitive substrate 100, therisk of defects in the dielectric layers 204 and/or 206 due to thebrittleness of the dielectric layers is reduced.

The conductive foils may be either power planes or ground planes, aslong as each capacitive element 210, 100, and 212 contains at least onepower plane and one ground plane separated by a dielectric layer. Thus,in one example, conductive foils 202 and 106 may be ground planes whileconductive foils 102 and 208 may be power planes. Alternatively,conductive foils 102 and 208 may be ground planes while conductive foils202 and 106 may be power planes. The conductive foils may bestructurally rigid sheets or they may be thin paper-like conductivelayers with little or no rigidity. For example, the conductive foils 202and/or 208 and/or the uncured or semi-cured dielectric layers 204 and/or206 may be flexible (non-rigid layers) before being coupled to the corecapacitive substrate 100. After coupling to the core capacitivesubstrate 100, the dielectric layers 204 and/or 206 may be cured andbecome more rigid and/or brittle.

In some implementations, additional patterning of clearances 214 maythen be formed on one or both of the conductive foils 202 and 208 byetching or other mechanical or chemical process.

Additional dielectric layers 216 and 218 and/or conductive foils 220 and222 may be similarly coupled onto the previous conductive foils 202 and208, respectively, to increase the capacitive density of the capacitivestack 200. Each of these additional conductive foils 220 and 222 mayalso be patterned with clearances. Note that in some implementations, anepoxy or filler paste may also be added on a conductive foil to fill-inthe clearances prior to coupling a subsequent dielectriclayer/conductive foil. In yet other implementations, the dielectriclayer 216 may be in an uncured or semi-cured state so that it fills theclearance 214 of the conductive foil onto which it is stacked andcoupled.

FIG. 3 illustrates a method for manufacturing a capacitive stack withhigh capacitive density. A planar core capacitive substrate is formedincluding a first dielectric core layer sandwiched between a firstconductive layer and a second conductive layer, wherein the capacitivecore substrate provides structural rigidity for coupling additionalconductive and dielectric layers 302. A pattern of one or moreclearances may be formed on the first conductive layer and/or secondconductive layer 304. The one or more clearances on the first conductivelayer may be filled with an epoxy or filler paste 306. The epoxy is thencured 308. The epoxy may then be planarized 310 to completely orsubstantially remove the excess epoxy or paste filler so that thesurface(s) of the first conductive layer may be exposed.

A first conductive foil may be coated with a second dielectric layerthat includes an uncured or semi-cured dielectric material loaded with ananopowder selected to achieve a desired dielectric constant 312. Anexposed surface of the second dielectric layer is then coupled to thefirst conductive layer 314 and the dielectric material of the seconddielectric layer is cured 316. In some implementations, additionalpatterning (e.g., power/ground plane clearances, delineation of discretecapacitive regions, etc.) may be formed. This patterning may be filledwith an epoxy and/or filler paste and excess epoxy or paste may beremoved by planarization.

Similarly, a second conductive foil may be coated with a thirddielectric layer that includes an uncured or semi-cured dielectricmaterial loaded with a nanopowder selected to achieve a desireddielectric constant 318. An exposed surface of the third dielectriclayer is coupled to the second conductive layer 320 and the dielectricmaterial of the third dielectric layer is cured 322. Note that thesecond and third dielectric layers may be simultaneously coupled to thefirst and second conductive layers, respectively, and cured. Additionalalternating layers of dielectric and conductive foils may be coupledonto the core capacitive substrate 324.

According to some examples, the core dielectric layer 104 may be between0.5 and 4 mils thick (or preferably between 0.5 and 2.0 mils) while thefirst and/or second conductive layers 102 and 106 may each be between0.5 and 6 mils thick. The combined thickness of the capacitive core(e.g., dielectric layer 102 and the first and second conductive layers102 and 106) may be between approximately 1.5 and 16 mils. The secondand/or third dielectric layers 204 and 206 may each be less than thethickness of first core dielectric layer 104. For instance, the secondor third dielectric layers 204 and 206 may each be coated to a thicknessof approximately between 0.08 and 1.5 mil. In some implementations, eventhinner dielectric layers 204 and 206 of 0.004 mil (for example) may beformed by using thin film and/or vapor deposition processes. In oneexample, the second or third dielectric layers 204 and 206 may each havea thickness of approximately 1 mil or less. The conductive foils 202,208, 220, and 222 may each have a thickness of between 0.12 and 6 mil.Note that additional conductive foils (e.g., between 0.12. and 6 milthick) and additional dielectric layers (e.g., between 0.004 and 1.5 milthick) may also be coupled to one or both sides of the capacitive stack.

In other examples, the core dielectric layer 104 may be approximately0.75 mil thick or more while the first and/or second conductive layers102 and 106 may each be between 1 and 4 mils thick. The second and/orthird dielectric layers 204 and 206 may each be less than the thicknessof first core dielectric layer 104. For instance, the second or thirddielectric layers 204 and 206 may each be coated to a thickness ofapproximately between 0.3 mil or less. The conductive foils 202, 208,220, and 222 may each have a thickness of between 0.12 and 1 mil thick.

Note that the present described methods may provide high-yield and/orhigh-volume manufacturing of capacitive stacks having ultra-thincapacitive layers stacked on a suitably rigid capacitive core. In priorart approaches, such thin capacitive layers have not been achieved aspart of a capacitive stack. This is because the ultra-thin layers ofdielectric 204 and 206 are quite brittle and difficult to handle ontheir own. Additionally, the technique described herein allows creatingcapacitive stacks having a greater capacitive constant per square inchthan prior art capacitive stacks. For example, the use of ultra-thincapacitive layers may allow achieving capacitive densities of a fewnano-Farads (e.g., 5 nano-Farads) to multiple micro-Farads per squareinch.

Method of Manufacturing and Testing a Capacitive Stack

Referring again to FIG. 2, making the dielectric layers 204 and/or 206thin or ultra-thin (e.g., 4 to 24 micron thick) increases the chance ofinclusions and/or voids that can cause electrical arcing or a shortbetween conductive layers/foils on opposite sides of a dielectric layer.In the prior art, a fault in an internal layer may not be identifieduntil the circuit board is completed or, worse yet, when it is inoperation. That is, conventional methods of manufacturing multilayercircuit boards typically couple all layers of the board in a singlestep. However, a fault in any one of the layers may cause the wholecircuit board to be discarded, thereby wasting materials.

To address this problem, one feature provides for sequentially addinglayers to the core capacitive substrate 100 and testing the integrity ofeach dielectric layer as it is added. The present approach forms thecapacitive stack 200 by adding one or more capacitive layers (i.e.,dielectric layers and conductive foils) either to one or both sides ofthe core capacitive substrate 100 and testing the integrity and/orelectrical characteristics of each capacitive layer as it is added,thereby detecting faults early. To facilitate testing of each capacitivelayer as it is added, test holes or clearances may be formed in theadded conductive and dielectric layers that allow probing or accessing acovered/concealed conductive layer. Note that a dielectric layer andconductive foil may be added simultaneously on both sides of a corecapacitive substrate and their integrity can be tested at the same time.

For instance, a first test hole 216 may be formed through the thirdconductive foil 202 and the first dielectric layer 204 to access thefirst conductive foil 102. The first test hole 216 may allow testing forfaults (e.g., inclusions or voids) in the first dielectric layer 204that may compromise the integrity of the stack 200. A resistance test orhigh-potential (hipot) test may be performed between conductive foils102 and 202. A relatively high voltage may be applied to one of theconductive layers 202, and a corresponding voltage is measured at theother conductive layer 102. The first test hole 214 may serve to couplea probe to the first conductive layer 102 to apply and/or measure avoltage thereon during the hipot test. If the dielectric layer 204 isdefective (i.e., if an electrical short exists between the twoconductive layers 102 and 202), electric current flows or arcs betweenthe conductive layers 102 and 202, and a corresponding voltage isdetected at the other conductive layer 102. If such fault is detected,the capacitive stack 200 may be discarded without wasting additionalmaterials and/or manufacturing resources.

Similarly, a second test holes 224 may be formed through the fourthconductive foil 208 and second dielectric layer 206, which can be usedfor testing for faults (e.g., inclusions or voids) in the seconddielectric layer 206.

In one implementation, the test holes 214 and/or 224 may be formed aftercoupling the dielectric layers 204 and/or 206 and conductive foils 202and/or 208 to the core capacitive substrate 100. Once coupled to thecore capacitive substrate 100, test holes 214 and/or 224 may be formedby using, for example, laser, drilling, and/or other means.

In yet other implementations, the test holes 216 and 218 may be formedbefore the dielectric layers 204 and/or 206 and conductive foils 202and/or 208 are coupled to the core capacitive substrate 100.

In other implementations, instead of using test holes to access or probea covered conductive foil or layer, the edges of the conductive layersmay be offset or staggered to have access to the different layers.Alternatively, the conductive layers may have tabs that protrude throughthe side of the capacitive stack to allow probing the individualconductive layers.

FIG. 4 illustrates a method for manufacturing an embedded corecapacitive stack according to one example. A structurally rigid corecapacitive substrate (e.g., core capacitive substrate 100 in FIG. 1) isformed including a first conductive layer and second conductive layercoupled on either side of a core first dielectric layer 402. The corecapacitive substrate (e.g., Faradflex BC24) may be rigid orsubstantially rigid by including a cured dielectric material in thefirst dielectric layer. The first dielectric layer may be cured eitherbefore or after coupling of the first and second conductive foils. Apower plane pattern (e.g., clearances) may be formed on the firstconductive layer 404. Similarly, a ground plane pattern may be formed onthe second conductive layer 406. The ground and/or power plane patternsmay be formed by known methods (e.g., etching, etc.) before or after thefirst and second conductive foils are coupled to the core firstdielectric layer. The ground and/or power plane patterns may formclearances for subsequent electrical paths and/or vias.

The core first dielectric layer may be tested to determine whether it isdefective 408. For instance, a hipot test may be performed between thefirst and/or second conductive layers to determine whether there anyfaults (e.g., inclusions and/or voids) in the core first dielectriclayer. If any faults are found, e.g., the first and second conductivelayers are shorted, the core capacitive substrate may be reworked ordiscarded 410 before additional materials, time, and/or labor arewasted.

The power and/or ground plane patterns (e.g., clearance) may then befilled with an epoxy and/or filler paste. In some implementations, theexcess epoxy and/or filler paste may be planarized or removed.

Thin conductive foils (e.g., ⅛ oz to 4 oz), each coated with an uncuredor partially cured dielectric layer (e.g., 4 to 24 micron thick) may bestacked or coupled on either side of the patterned core capacitivesubstrate to form a capacitive stack. The dielectric layer for eachconductive foil may be loaded with a nanopowder to increase thedielectric constant. As they are added to the core capacitive substrate(either on one side or both sides of the core capacitive substrate atonce), the dielectric layers may be tested for faults (e.g., inclusionsor voids) that compromise the electrical integrity of the overallcapacitive stack (e.g., by causing shorts or arcing between conductivelayers on either side of a dielectric layer).

For example, a first conductive foil is then coated with an uncured orsemi-cured dielectric material loaded with a nanopowder that forms asecond dielectric layer 412. The first conductive foil and the seconddielectric layer are stacked onto the first conductive layer 414. Forexample, the first conductive foil and second dielectric layer may belaminated under temperature and/or pressure to the core capacitivesubstrate. In coupling the first conductive foil and second dielectriclayer to the core capacitive substrate, heat and/or pressure may serveto cure the second dielectric layer. A ground/power pattern may also beformed on the first conductive foil 416 to achieve a desiredpower/ground configuration. Along with the electrical patterns, a blindtest hole may be formed through the first conductive foil and seconddielectric layer. This test hole may be located along a perimeter region(e.g., out of the circuit pattern area) and allow probing of the firstconductive layer. In one example, the test hole(s) or clearances througha conductive foil and/or dielectric layer may be formed by aUltra-Violet (UV) YAG or C02 laser.

In an alternative embodiment, the first conductive layer may be coatedwith the uncured or semi-cured dielectric material loaded with thenanopowder to form the second dielectric layer and the first conductivefoil may then be coupled (e.g., laminated) to the second dielectriclayer. In still another embodiment, the first conductive layer and thefirst conductive foil may both be coated with a dielectric material andthe surfaces of the two dielectric coats may be coupled (e.g.,laminated) together.

The second dielectric layer may then be tested or validated to ascertainits electrical integrity, e.g., whether there is a defect in the seconddielectric layer 418. For example, a hipot test may be performed betweenthe first conductive foil and the first conductive layer to determinewhether they are electrically isolated from each other. For instance, aprobe may electrically contact the first conductive layer (through atest hole in the first conductive foil) to determine whether a voltageapplied to one conductive foil/layer is measured in the other conductivefoil/layer. If the test indicates a defect in the second dielectriclayer, the capacitive stack may be discarded 420. This pre-testing maybe performed as layers are added to the capacitive stack, therebyidentifying faulty or unreliable capacitive stacks early in theirmanufacturing process.

Similarly, a second conductive foil may also be coated with the uncuredor semi-cured dielectric material loaded with the nanopowder to form athird dielectric layer 422. An exposed surface of the third dielectriclayer is then coupled (e.g., laminated) to the second conductive layerto form a third capacitive element 424. In an alternative embodiment,the second conductive layer may be coated with the uncured or semi-cureddielectric material loaded with the nanopowder to form the thirddielectric layer and the second conductive foil may then be coupled(e.g., laminated) to the exposed surface of the third dielectric layer.In still another embodiment, the second conductive foil and the secondconductive layer may both be coated with the uncured or semi-cureddielectric material and the exposed surfaces of the two dielectric coatsmay be coupled together.

The third dielectric layer may then be similarly tested for defects 426.For example, a hipot test may be performed between the second conductivefoil and the second conductive layer to ascertain whether they areelectrically isolated from each other. If the test indicates a defect inthe third dielectric element, the capacitive stack may be discarded 428.

The first and second conductive foils and second and third dielectriclayers may be added to the capacitive stack at the same time. The secondand third dielectric layers may also be tested at the same time.

One or more capacitive elements (e.g., conductive foils and dielectriclayers) may be added to the capacitive stack and each capacitive elementmay be tested for defects as it is added to the capacitive stack 430.

Additionally, a conductive foil may be patterned to define one or moreseparate regions that may be utilized as distinct capacitive elements.Each of these separate regions may be tested to ascertain whether theircorresponding dielectric layer is not defective (as discussed above).

Any number of capacitive layers may be added to the top and/or bottom ofthe first core capacitive substrate 502 and tested as they are added.For example, FIG. 5 illustrates a capacitive stack 500 including a corecapacitive element 502 (conductive layers/foils 502 a and 502 c, anddielectric layer 502 b) with a dielectric/conductive layer pair 504(i.e., dielectric layer 504 a and conductive foil 504 b) on one side andtwo dielectric conductive layer pairs (i.e., dielectric layer 506 b andconductive foil 506 a and dielectric layer 508 b and conductive foil 508a) on an opposite side.

Capacitive Stack With Isolated Planar Capacitive Elements

Another novel feature provides a printed circuit board including a corecapacitive stack configurable to supply a parallel planar capacitiveelement having high capacitance density or a plurality of segregated,device-specific decoupling capacitive elements. Thus, the capacitivestack may be selectively configured to provide high capacitance or aplurality of segregated embedded planar capacitors or discrete valuecapacitors with specific value depending on an implementation.

FIG. 6 illustrates how a core capacitive stack 600 may be configured toprovide a planar capacitive element having high capacitive densityaccording to one example. The capacitive stack 600 includes a corecapacitive element 602, a first capacitive element 604, and a secondcapacitive element 606. The core capacitive element 602 may include acured dielectric layer 612 sandwiched between a first and a secondconductive layers (foils) 610 and 614. The first capacitive element 604may be formed by a third conductive layer 616 coated with (or coupledto) a second dielectric layer 618. Similarly, the second capacitiveelement 606 may be formed by a fourth conductive layer 620 coated with athird dielectric layer 622.

A first electrically conductive via 624 is coupled to the thirdconductive layer 616 and second conductive layer 614, where both layersare parallel ground layers. A clearance 626 electrically isolates thevia 624 from the first conductive layer 610. A second clearance 628electrically isolates the via 624 from the fourth conductive layer 620.

A second electrically conductive via 630 is coupled to the firstconductive layer 610 and fourth conductive layer 620, where both layersare parallel power layers. A third clearance 634 electrically isolatesthe via 630 from the second conductive layer 614. An fourth clearance632 electrically isolates the via 630 from the third conductive layer616.

In this example, an embedded planar capacitor having high capacitivedensity is formed by electrically connecting the second and thirdconductive layers 614 and 616 (coupled in parallel) and the first andfourth conductive layers 610 and 620 (also coupled in parallel). Thus, adevice may be coupled to this multilayer embedded planar capacitorformed between the combination of the second and third conductive layers614 and 616 and the first and fourth conductive layers 610 and 620.

Multiple levels of parallel layers may be added to the embeddedcapacitive stack 600 to build very high capacitive density, therebyachieving a potentially much higher capacitance per square inch thancompeting alternatives.

In one example, the dielectric layer 612 may be (or include) adielectric material (e.g., Faradflex 24, Dupont Hk, etc.) approximatelytwenty-four (24) micrometers thick. The dielectric layers 618 and 622may each be a nanopowder loaded dielectric material between two (2) andtwenty-four (24) micrometers thick. The total thickness of thecapacitive stack 600 may be between four (4) and eight (8) thousandthsof an inch (mil). The nanopowder may be either a fired or prefiredmaterial, such as Barium Titanate for example. Note that the dielectricmaterial and/or nanopowder material properties can be adjusted toachieve different levels of performance.

The same capacitive stack 600 may be configurable to provide a pluralityof segregated, device-specific decoupling capacitive elements to one ormore devices on the circuit board. Thus, instead decoupling of allelectronic devices on a PCB with a shared embedded capacitance, thisfeature provides multiple isolated capacitive elements capable of beingcoupled to different electronic devices. Additionally, a singleelectronic device may have different leads coupled to differentcapacitive elements in the capacitive stack 600.

FIG. 7 illustrates how capacitive stack 500 may be configured to providea plurality of segregated planar capacitive elements according to oneexample. In this example, a first capacitive element 702 may be formedbetween the first conductive layer 610 and the third conductive layer616. A via 706 is coupled to the first conductive layer 610 and a firstclearance 708 to allow an electronic device to be decoupled between thefirst conductive layer 610 and third conductive layer 616.

A second capacitive element 704 may be similarly formed between thesecond conductive layer 614 and the fourth conductive layer 620. A via710 is coupled to the second conductive layer 614 and a passes throughclearance 712 to allow an electronic device to be decoupled betweensecond conductive layer 614 and the fourth conductive layer 620.

A third capacitive element 602 may be similarly formed by the corecapacitive substrate 602 (i.e., between the first conductive layer 610and the second conductive layer 614). The via 710 is coupled to thesecond conductive layer 614 and passes through clearances 714 and 716 toallow an electronic device to be decoupled between the second conductivelayer 614 (through via 710) and the first conductive layer 610 (throughvia 706).

In this manner, the four-conductive layer capacitive stack 600 may beconfigured to provide three (3) separate planar capacitors 702, 704, and602. This allows for the segregation of noisier components (devices)from other components (devices) requiring quieter power distribution.

This concept of configuring a capacitive stack to provide one or moredesired capacitive elements may be expanded depending on the number ofavailable conductive layers in a stack and the decoupling requirementsof circuit components.

FIG. 8 illustrates an example of how a capacitive stack 800 may beconfigured to provide a plurality of isolated capacitive planes todecouple electronic components. The capacitive stack 800 may include aplurality of alternating ground and power layers formed by a pluralityof conductive foils 812, 814, 816, and 818 with dielectric layers inbetween. The capacitive stack 800 may be embedded or serve as the corefor additional circuit layers 838 and 842 of a multi-layer substrate.These additional circuit layers 838 may be coupled on one or both planarsurfaces of the capacitive stack 800. Thus, the capacitive stack 800 maybe sandwiched between additional circuit layers. The stack 800 mayprovide one or more power and/or ground planes of one or more voltagesfor the circuit layers 838 and 842 and/or circuit components 808 and810. The stack 800 may also provide one or more decoupling capacitiveelements to the circuit components 808 and 810

A first leg 830 of a first component A 808 (e.g., integrated circuitdevice, etc.) is electrically coupled to a first conductive foil 812through a conductive via 840. A second leg 832 of the first component A808 is electrically coupled to a second conductive foil 814 by a via802. The via 802 may be electrically isolated from the first conductivefoil 812 by a clearance 820. A first capacitive element 813 is formedbetween the first and second conductive foils 812 and 814 providingbypass filtering to the first component A 808.

A second component B 810 may have a first leg 834 electrically coupledto a third conductive foil 816 by a via 804. The via 804 may beelectrically isolated from the first conductive foil 812 by a clearance822 and isolated from the second conductive foil 814 by a gap and/orclearance 825. A second leg 836 of the second component B 810 iselectrically coupled to a fourth conductive foil 818 by a via 806. Thevia 806 may be electrically isolated from the other conductive foils812, 814, and 816 by clearances 824, 826 and 828. A second capacitiveelement 815 is formed between the third conductive foil 816 and thefourth conductive foil 818 providing bypass filtering to the secondcomponent B 810.

By coupling the first component A 808 and the second component B 810 tothe capacitive stack 800 in the way shown and described, the firstcomponent A 808 is decoupled by the first capacitive element 813 that isseparate from the second capacitive element 815 which is used todecouple the second component B 810. Therefore, if the first component A808 is a high noise device, its decoupling capacitive element 813 can beisolated from other devices so that it does not interfere with theiroperation. In this manner, various electronic devices on a circuit boardmay be isolated from each other, by having different embedded decouplingcapacitive elements. In fact, different legs for a single electroniccomponent may be decoupled by different embedded capacitive elements.Additionally, in the example of FIG. 8, a third capacitive element maybe formed between the second conductive foil 814 and the thirdconductive foil 816.

Note that the first capacitive element 813 may provide power at a firstvoltage level to the first component A 808 while the second capacitiveelement 815 may provide power at a second voltage level to the secondcomponent B 810. In various implementations, the first and secondvoltage levels may be the same or they may be different.

FIG. 9 illustrates another example of how a capacitive stack 900 may beconfigured to form a plurality of distinct bypass capacitors to decoupleelectronic components. The capacitive stack 900 may include a pluralityof alternating ground and power layers formed by conductive foils 912,914, 916, 918, and 920 with dielectric layers in between them. Thecapacitive stack 900 may be constructed in a similar manner as thecapacitive stacks illustrated in FIGS. 1, 2, 3 and/or 4. The capacitivestack 900 may be embedded or serve as the core for additional circuitlayers 942 and/or 944 of a multi-layer substrate. These additionalcircuit layers 942 and/or 944 may be coupled on one or both planarsurfaces of the capacitive stack 900. Thus, the capacitive stack 900 maybe sandwiched between circuit layers 942 and 944 on either side of thecapacitive stack 900.

A first leg 932 of a first component A 902 (e.g., integrated circuitdevice) is electrically coupled to second and fourth conductive foils914 and 918 by a via 906. The via 906 may be electrically isolated fromfirst and third conductive foils 912 and 916 by clearances 924 922. Asecond leg 934 of the first component A 902 is electrically coupled tothird and fifth conductive foils 916 and 920 by a via 908. The via 908may be electrically isolated from conductive foils 912, 914, and 918 byclearances 930, 926 and 928. The first component A 902 may thereby beelectrically coupled to a first capacitive element 917 including aplurality of capacitive elements in parallel. By connecting the firstcomponent A 902 to a plurality of capacitive elements in parallel, thedecoupling capacitance to the first component A 902 may be increasedwithout the need for an additional surface-mounted discrete capacitor tothe circuit board assembly.

A second component B 904 may have a first leg 936 electrically coupledto the first conductive foil 912 by a conductive via 944. A second leg938 of the second component B 904 is electrically coupled to the secondconductive foil 914 by a via 910. The via 910 may be electricallyisolated from the conductive foil 912 by a clearance 940. The secondcomponent B 904 is thus coupled to a second capacitive element 915 thatis separate from the first capacitive element 917 of the first componentA 902. If the first component A 902 is a high noise device requiringgreater capacitance, this configuration provides the increasedcapacitance and segregates the bypass first capacitive element 917 ofthe first component A 902 from the second capacitive element 915 of thesecond component B 904. Thus, the noise produced by first component A902 does not interfere with second component B 904.

Although the embodiments discussed in FIGS. 8 and 9 illustrate theelectronic component situated on one side of the capacitive stacks 800and 900, components may be coupled on both sides of the capacitivestacks.

FIG. 10 illustrates yet another example of how a capacitive stack 1000may be configured to form a plurality of distinct bypass capacitors todecouple electronic components on double-sided circuit board. Thecapacitive stack 1000 may include a plurality of alternating ground andpower layers formed by a plurality of conductive foils 1012, 1014, 1016,and 1018 with dielectric layers in between. The capacitive stack 1000may be embedded or serve as the core for additional circuit or signallayers 1038 and 1039 of a multi-layer substrate. Thus, the capacitivestack 1000 may be sandwiched or embedded between additional circuit orsignal layers 1038 and 1039.

A first circuit component A 1008 may be mounted on first circuit layers1038. A first leg 1030 of the first component A 91008 (e.g., integratedcircuit device, etc.) is electrically coupled to a first conductive foil1012 through a conductive via 1040. A second leg 1032 of the firstcomponent A 1008 is electrically coupled to a second conductive foil1014 by a via 1002. The via 1002 may be electrically isolated from thefirst conductive foil 1012 by a clearance 1020. A first capacitiveelement 1013 is formed between the first and second conductive foils1012 and 1014 providing bypass filtering to the first component A 1008.Similarly, a third leg 1034 of component A 1008 is electrically coupledto a third conductive foil 1016 by a via 1004. The via 1004 may beelectrically isolated from the first conductive foil 1012 by a clearance1022 and isolated from the second conductive foil 1014 by clearance1025. A fourth leg 1036 of the first component A 1008 is electricallycoupled to a fourth conductive foil 1018 by a via 1006. The via 1006 maybe electrically isolated from the other conductive foils 1012, 1014, and1016 by clearances 1024, 1026 and 1028. A second capacitive element 1015is formed between the third conductive foil 1016 and the fourthconductive foil 1018 providing bypass filtering to the first component A1010.

A second circuit component B 1010 may mounted on second circuit layers939. A first leg 942 electrically coupled to a third conductive foil1016 by a via 1046. The via 942 may be electrically isolated from thefourth conductive foil 918 by a clearance 1050. A second leg 1044 of thesecond component B 1010 is electrically coupled to a second conductivefoil 1014 by a via 1048. The via 1048 may be electrically isolated fromthe other conductive foils 1016 and 1018 by clearances 1052 and 1054. Asecond capacitive element 1056 is formed between the second conductivefoil 1014 and the third conductive foil 1016 providing bypass filteringto the second component B 1010.

The example illustrated in FIG. 10 allows coupling circuit component A1008 to two segregated capacitive elements 1013 and 1015 while couplingcircuit component B 1010 to another segregated capacitive element 1056.

Clearances isolation gaps may be formed in each conductive layer at anytime during fabrication, such as prior to coupling the conductive foilto the capacitive stack, immediately after adding the conductive foil onthe capacitive stack, and/or after all conductive foils are added to thecapacitive stack. The clearances and/or isolation gaps may be formedusing any method known in the industry such as drilling, punching,laser, and/or etching techniques.

FIG. 11 illustrates a method for forming isolated decoupling capacitiveelements in a capacitive stack according to one example. A planarcapacitive stack including multiple electrically isolated conductivelayers is formed 1102. Such capacitive stack may be formed as describedand illustrated in FIGS. 1, 2, and/or 3, for example. A first capacitiveelement having a first desired capacitive density is then formed betweentwo conductive layers of the capacitive stack 1104. A first circuitcomponent may be coupled to the first capacitive element 1106. In oneexample, the first capacitive density of the first capacitive elementmay be selected to provide bypass capacitance according to theelectrical characteristics and/or needs of the first circuit component.A second capacitive element having a second desired capacitive densityis formed between two conductive layers of the capacitive stack, whereinthe second capacitive element is electrically isolated from the firstcapacitive element 1108. A second circuit component may be to the secondcapacitive element 1110. The second capacitive density may be selectedto provide bypass capacitance according to the electricalcharacteristics and/or needs of the first circuit component. In someimplementations, the first capacitive density and second capacitivedensity may be the same. In other implementations, the first and secondcapacitive densities may be different.

Additional capacitive elements may be similarly formed between two ormore conductive layers of the capacitive stack, wherein the additionalcapacitive elements are electrically isolated from the first and secondcapacitive elements and from each other 1112. Additional circuitcomponents may be coupled to the additional capacitive elements 1114.

In order to form each capacitive element, clearances may be formed inone or more layers of the capacitive stack either as each layer is addedto the capacitive stack or after a plurality of layers have been addedto the capacitive stack.

In some implementations, the planar capacitive stack described in FIG.11 may be formed by the method(s) illustrated in FIGS. 1, 2, 3, and/or4.

Embedded Discrete Capacitors

Yet another novel aspect provides for forming discrete capacitors withinan embedded capacitive stack that may be used in a multilayered printedcircuit board to provide localized decoupling capacitance to one or moredevices. For example, a capacitive stack may be constructed as asubassembly and tested for defects prior to embedding into a circuitboard. The discrete stacked capacitor may be formed by electricallyisolating an area or region of a conductive layer of the capacitivestack. A desired capacitive value may be obtained by appropriatelysizing the region or area for a given capacitive density of thedielectric layer(s).

FIG. 12 illustrates an example of how one or more layers of a capacitivestack 1200 may be divided to provide additional decoupling capacitanceto one or more circuit components. The capacitive stack 1200 may beformed, for example, as described in FIGS. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10and/or 11. For instance, a core capacitive element 1214, including adielectric layer 1202 sandwiched between conductive layers 1204 and1206, may serve as a base on which to couple additional dielectriclayers 1208 and 1210 and conductive layers 1206 and 1212. The capacitivestack 1200 may include a plurality of conductive and dielectric layers,power/ground patterns of clearances that define one or more capacitiveelements that may be used without further fabrication or alteration.

One or more of the conductive layers may be patterned to define separatecapacitive regions. For example, a first conductive layer 1206 may bepatterned, etched, or otherwise processed to define regions 1216, 1217and 1218 that are electrically isolated from the remaining portions ofthe first conductive layer 1206. Once the capacitive stack 1200 isformed and/or tested for defects, it may be embedded in a larger printedcircuit board.

Independent of the capacitance provided by the first conductive layer1206, the electrically isolated regions 1216, 1217 and/or 1218 may alsoserve to independently decouple one or more electronic devices. Thediscrete capacitors are formed between the isolated regions 1216, 1217,and 1218 and a corresponding opposite layer (e.g., conductive layer1204). The amount of capacitance provided by the isolated regions 1216,1217 and 1218 is defined by the area of each region (e.g., length xwidth) and the capacitive density of the dielectric layer (e.g.,dielectric layer 1208). In this manner, electronic devices may bematched with a desired capacitive value defined by an isolated region.

The isolated regions 1216, 1217, and 1218 may also be tested forreliability after each layer is added to the capacitive stack by makinga clearance (e.g., hole) to the next adjacent conductive layer anddetermining whether there is a short with the isolated regions 1216,1217, and 1218.

Note that the isolated regions for the embedded discrete capacitors maybe defined by etching or other mechanical or chemical processes as eachconductive layer/foil is added to the capacitive stack. The methodsdescribed herein allow capacitors of any shape and/or size to be formedon the conductive layers/foils thereby reducing the need for surfacemounted capacitors and, consequently, potentially allowing for circuitboards of small surface area.

FIG. 13 illustrates yet another example of how one or more conductivelayers of a capacitive stack 1302 may be divided into different areas orregions that are electrically isolated from other regions on the sameconductive layer. In this example, the conductive layer 1300 in thecapacitive stack 1302 may be divided into a plurality of regions 1304,1306, 1308, and 1310. When embedded into a multi-layer circuit board orsemi-conductor packaging, these separate regions 1304, 1306, 1308, and1310 may operate at different voltages.

FIG. 14 illustrates a method for manufacturing a circuit board having anembedded capacitive stack according to one example. A capacitive stackis formed having multiple conductive layers defining one or more planarcapacitive elements 1402. In one example, the capacitive stack is formed(e.g., as illustrated in FIGS. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,and/or 13). Such capacitive stack may serve as the core onto whichcircuit layers may be coupled on either side of the capacitive stack. Afirst electrically isolated region is defined within a first conductivelayer of the capacitive stack 1404. This electrically isolated regionmay be formed or defined during the process of stacking the firstconductive layer onto the capacitive stack. One or more circuit boardlayers may be coupled to the capacitive stack 1406. A first electricallyconductive via is formed extending from an outer layer of the circuitboard to the first conductive layer of the capacitive stack 1408. Asecond electrically conductive via is formed extending from the outerlayer of the circuit board to the first electrically isolated region inthe first conductive layer 1410. A third electrically conductive via isformed extending from the outer layer of the circuit board to a secondconductive layer of the capacitive stack 1412. A first bypass capacitormay be defined between the first and second conductive layers and asecond bypass capacitor may be defined by the first electricallyisolated region and the second conductive layer 1414. A first circuitcomponent may be coupled between the first and third vias to provide thefirst circuit component a first bypass capacitance 1416. Similarly, asecond circuit component may be coupled between the second and thirdvias to provide the second circuit component a second bypass capacitance1418. In some implementations, different electrical legs of a singlecircuit component may be decoupled by the first and second bypasscapacitances. The area of the first electrically isolated region may beselected to obtain a desired capacitance.

Embedded Capacitive Stack for Chip-Scale Packaging

As noted in FIGS. 6, 7, 8, 9 and/or 10, the presently disclosedcapacitive stack embeds multiple bypass capacitive layers within a coresubstrate for a circuit board or electronic platform, thereby reducingthe parasitic inductance. That is, using embedded capacitors instead ofsurface mounted discrete capacitors reduces the path length signalstravel which, in turn, reduces parasitic inductance. Consequently,various implementations of the capacitive stack disclosed reduce thelength of the signal path by moving the capacitive elements closer tocircuit components.

In the prior art, semiconductor devices are typically decoupled byseparate discrete capacitors located on a circuit board on which thesemiconductor packages are coupled.

In one example of the present claimed capacitive stack, the capacitivestack is embedded within the semiconductor packaging. Because the methoddescribed above allows making a very thin capacitive stack, it permitsembedding the capacitive elements inside the semiconductor packagingrather than on a circuit board.

FIG. 15 illustrates one example of how a capacitive stack may be usedwithin a chip-scale package 1500 to provide localized capacitance to asemiconductor device 1502. The chip-scale package 1500 may include acapacitive stack comprising a core capacitive element 1504 (i.e.,dielectric layer 1514 sandwiched between conductive layers 1520 and 1522and a plurality of dielectric layers 1512 and 1516 and conductive foils1510 and 1524. In this example, the capacitive stack is sandwichedbetween one or more circuit layers 1506 and 1508. A semiconductorcircuit 1502 may be coupled on a first circuit layer 1506. The firstcircuit layer 1506 may be patterned to allow electrically conductivevias 1526, 1528, 1530, and 1534 to couple to different legs of thesemiconductor circuit 1502.

In this example, the semiconductor circuit 1502 is coupled to twodistinct capacitive elements in the capacitive stack. A first capacitiveelement 1542 is formed by a first dielectric layer 1512 sandwichedbetween a second conductive layer 1510 and a first conductive foil 1520.A second capacitive element 1544 is formed by a second dielectric layer1516 sandwiched between a second conductive foil 1522 and a thirdconductive foil 1524. A first via 1528 and a second via 1530 couple twodifferent legs of the semiconductor circuit 1502 to the first capacitiveelement 1542. A third and fourth vias 1526 and 1534 couple two differentlegs of the semiconductor circuit 1502 to the second capacitive element1544. In this manner, the bypass capacitance for the semiconductorcircuit 1502 may be housed within the chip-scale package 1500.

The chip-scale package 1500 may then be coupled on a circuit board 1536.For example, a ball grid array may be used to couple a plurality ofbumps 1538 on the chip-scale package 1500 to corresponding pads 1540 onthe circuit board 1536.

It should be clearly understood that the features described herein maybe implemented on circuit layers of different dimensions and/ormaterials. For instance, the (a) method of manufacturing and testing acapacitive stack, (b) method of providing a plurality of isolated planarcapacitive elements, and/or (c) embedded stacked capacitor (orcapacitive stack) may each be implemented in a multilayer board, siliconsubstrate, semiconductor device, chip-scale package, etc. In someimplementations, the capacitive stack may be implemented as part of amultilayer circuit board on which electronic devices may be coupled. Inother implementations, the capacitive stack may be implemented as partof silicon substrate (e.g., wafer) for semiconductors on whichintegrated circuits and/or microelectronic devices may be coupled orformed.

One or more of the components, steps, and/or functions illustrated inFIGS. 1-15 may be rearranged and/or combined into a single component,step, and/or function or in separated into several components, steps,and/or functions without departing from the invention. Additionalelements, components, steps, and/or functions may also be added withoutdeparting from the invention.

While certain exemplary embodiments have been described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative of and not restrictive of the scope of theinvention, and that this invention not be limited to the specificconstructions and arrangements shown and described, since various othermodifications are possible. Those skilled, in the art will appreciatethat various adaptations and modifications of the just describedpreferred embodiment can be configured without departing from the scopeand spirit of the invention. Therefore, it is to be understood that,within the scope of the appended claims, the invention may be practicedother than as specifically described herein.

1. A capacitive stack with high capacitive density, comprising: a planarcore capacitive substrate including a first core dielectric layersandwiched between a first conductive layer and a second conductivelayer, wherein the core capacitive substrate provides structuralrigidity for coupling additional conductive and dielectric layers; asecond dielectric layer having a first planar surface coupled to thefirst conductive layer, the second dielectric layer being thinner thanthe first core dielectric layer and including a dielectric materialloaded with a nanopowder selected to achieve a desired dielectricconstant; and a first conductive foil coupled to a second planar surfaceof the second dielectric layer; wherein the thickness of the seconddielectric layer is less than the thickness of first dielectric layer.2. The capacitive stack of claim 1 further comprising: one or morealternating conductive foils and dielectric layers coupled on at leastone side of the capacitive core substrate.
 3. The capacitive stack ofclaim 1 wherein the first and second conductive layers and the firstconductive foil are alternating power and ground planes.
 4. Thecapacitive stack of claim 1 wherein at least one of the first and secondconductive layers include a pattern of one or more clearances.
 5. Thecapacitive stack of claim 1, wherein the second dielectric layer iscoated to a thickness of approximately between 0.004 and 1.25 mil. 6.The capacitive stack of claim 1, wherein the second dielectric layer iscoated to a thickness of approximately 0.3 mil or less.
 7. Thecapacitive stack of claim 1, wherein the first conductive foil is anultra-thin foil having a thickness of between 0.12 and 1 mil.
 8. Thecapacitive stack of claim 1, wherein the second dielectric layerprovides a capacitive density of between five (5) and sixty (60)nano-Farads per square inch.
 9. A capacitive stack, comprising: a planarcapacitive core substrate including a first dielectric layer sandwichedbetween a first conductive layer and a second conductive layer, whereinthe first dielectric layer provides structural rigidity for additionalconductive and dielectric layers; a second dielectric layer sandwichedbetween a first conductive foil and the first conductive layer, whereinthe second dielectric layer is thinner than the first dielectric layerand includes dielectric material loaded with a nanopowder; a firstisolated capacitive element defined between the first conductive layerand the second conductive layer; and a second isolated capacitiveelement defined between the first conductive layer and the firstconductive foil.
 10. The capacitive stack of claim 9, furthercomprising: a third dielectric layer sandwiched between the secondconductive layer and a second conductive foil; and a third isolatedcapacitive element defined between the second conductive layer and thesecond conductive foil.
 11. The capacitive stack of claim 10 wherein thefirst conductive layer and second conductive foil serve as power layerswhile the second conductive layer and first conductive foil serve asground layers.
 12. The capacitive stack of claim 10 further comprising:a first electrically conductive via coupled between the first conductivelayer and second conductive foil; and a second electrically conductivevia coupled between the second conductive layer and first conductivefoil, wherein a capacitive element having increased capacitive densityis formed between the first conductive layer and second conductive foiland the second conductive layer and first conductive foil.
 13. Thecapacitive stack of claim 9 wherein the thickness of the seconddielectric layer is less than the thickness of first dielectric layer.14. The capacitive stack of claim 9 wherein the first dielectric layeris approximately between 0.5-4 mils thick, the first and secondconductive layers are each approximately between 0.5-6 mils thick, thesecond dielectric layer is approximately between 0.8 and 1 mil thick,and the first conductive foil is approximately between 0.25-1.5 milsthick.
 15. The capacitive stack of claim 9 wherein the first conductivefoil includes a first region electrically isolated from the firstconductive foil, wherein the first region and the first conductive layerdefine a first discrete capacitive element.
 16. The capacitive stack ofclaim 15 wherein the area of the first region is selected to obtain adesired capacitive value for the first discrete capacitive element. 17.An electronic interconnect platform, comprising: a planar embeddedcapacitive stack including a planar capacitive core substrate includinga first dielectric layer sandwiched between a first conductive layer anda second conductive layer, wherein the first dielectric layer providesstructural rigidity for additional conductive and dielectric layers, oneor more alternating dielectric layers and conductive foils coupled on atleast one side of the planar capacitive core substrate, wherein the oneor more dielectric layers include a dielectric material loaded with ananopowder; wherein the first and second conductive layers and the oneor more alternating dielectric layers and conductive foils areconfigurable to operate as segregated capacitive elements; and one ormore signal layers coupled on at least one side of the embeddedcapacitive stack.
 18. The electronic interconnect platform of claim 17further comprising: a first circuit component coupled to an exteriorsignal layer and electrically coupled to a first segregated capacitiveelement formed between a first conductive foil and the first conductivelayer in the embedded capacitive stack.
 19. The electronic interconnectplatform of claim 18 wherein the first circuit component is furthercoupled to a second segregated capacitive element formed between thefirst conductive layer and a second conductive foil in the embeddedcapacitive stack, the second segregated capacitive element beingdistinct from the first segregated capacitive element.
 20. Theelectronic interconnect platform of claim 18 further comprising: achip-scale package housing the planar embedded capacitive stack, the oneor more signal layers, and the first circuit component
 21. Theelectronic interconnect platform of claim 17 wherein the first andsecond conductive layers and one or more conductive foils arealternating power and ground planes.
 22. The electronic interconnectplatform of claim 17 wherein a first region in a third conductive foilfrom among the one or more conductive foils is electrically isolatedfrom the third conductive foil, wherein the first region and an adjacentconductive foil define a first discrete capacitor electrically isolatedfrom the remaining portions of the third conductive foil.